As transfer protocols for transferring electronic files or content, a TCP protocol has been in widespread use. In the TCP protocol, when TCP segment data (hereinafter referred to as “TCP-DATA”) of a transmission unit, which is transmitted by a transmitter terminal, normally arrives at a receiver terminal in a TCP layer of a network, a delivery acknowledgement (TCP acknowledgement), hereinafter referred to as “TCP-ACK”) as a TCP protocol is returned from the receiver terminal to the transmitter terminal to ensure reliability.
Also, the following communication efficiency is conducted in the TCP protocol. In the transmitter terminal, even if the TCP-ACK is not received under a window control, TCP-DATA is continuously transmitted. In the receiver terminal, a technique called “delayed acknowledgement (delayed ack)” is used. In general, the receiver terminal is implemented to transmit the TOP-ACK upon receiving two segments of TCP-DATA having the maximum length (for example, refer to Non Patent Literature 1).
Also, as data communication means, wireless LAN systems have been in widespread use from the viewpoint of convenience. FIG. 14 illustrates an example of a data communication system when a wireless LAN is used. A terminal (wireless LAN terminal) 1501 using the wireless LAN is located in a wireless LAN communication area 1504 that enables communication with a wireless LAN access point 1502, and connected to a communication network 1505 through the wireless LAN access point 1502.
Also, the wireless LAN access point 1502 is generally connected to the communication network 1505 via wired media such as Ethernet (registered trademark) or an optical fiber. The communication network 1505 includes, for example, the internet, the intranet, a residential network, and a public infrastructure network that is managed by a carrier. Also, the communication network 1505 is connected with a communication partner terminal 1503, and the wireless LAN terminal 1501 and the communication partner terminal 1503 enable data communication with each other through the communication network 1505 according to the TCP protocol.
The wireless LAN system generally in widespread use is of a system stipulated in IEEE 802.11. Also, an access algorithm realized in an MAC layer is based on a CSMA/CA (carrier sense multiple access with collision avoidance) system (for example, refer to Non Patent Literature 2). In the CSMA/CA system, a terminal that is going to transmit data implements carrier sense for determining whether communication media (wireless media in this case) is used, or not.
A transmission right of data is acquired only when that the communication media is not used in a predetermined period (carrier free) can be confirmed as a result of the carrier sense. When transmission from another terminal is detected during the carrier sense, transmission from a subject terminal is delayed until the carrier free is detected (for example, refer to Non Patent Literature 2).